fpga: region: rename some functions prior to moving

Rename some functions that will be moved to
of-fpga-region.c.  Also change some parameters
and export a function to help with refactoring.

This is a step towards the larger goal of separating
device tree support from FPGA region common code.

* fpga_region_get_manager -> of_fpga_region_get_mgr

* add 'of_' prefix to the following:
  * fpga_region_find
  * fpga_region_get_bridges
  * fpga_region_notify_pre_apply
  * fpga_region_notify_post_remove),
  * fpga_region_probe/remove

Parameter changes:
* of_fpga_region_find
  change parameter to be the device node of the region.
* of_fpga_region_get_bridges
  change second parameter to FPGA image info.

Export of_fpga_region_find as well.

Signed-off-by: Alan Tull <atull@kernel.org>
Acked-by: Moritz Fischer <mdf@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>